This invention relates in general to power take-off units for selectively providing rotational power to a driven accessory provided on an engine driven vehicle. More specifically, this invention relates to an improved structure for a housing for such a power take-off unit that has a hydraulic manifold formed integrally therein.
Power take-off units are well known mechanical devices that are commonly used in conjunction with sources of rotational energy, such as vehicle engines and transmissions, for rotatably driving driven accessories. For example, power take-off units are commonly used in a variety of industrial and agricultural vehicles for operating hydraulic pumps that, in turn, operate hydraulically driven accessories, such as plows, trash compactors, lifting mechanisms, winches, and the like.
A typical power take-off unit includes a rigid housing that is mounted on a case of a transmission of the vehicle. The mating surfaces of the housing of the power take-off unit and the case of the transmission having relatively large openings formed therethrough. The housing of the power take-off unit rotatably supports an input gear, an output gear that meshes with the input gear, and an output shaft that is adapted to be connected to the driven accessory. A portion of the input gear extends outwardly through the openings in the housing of the power take-off unit and the case of the transmission into meshing engagement with one of the transmission gears that is constantly driven by the vehicle engine. As a result, the input gear and the output gear of the power take-of unit are constantly rotatably driven by the transmission gear and, thus, the engine of the vehicle.
In some instances, the output gear is directly connected to the output shaft such that the output shaft is also constantly rotatably driven. In other instances, however, a clutch assembly is provided for selectively connecting the output gear to the output shaft to permit intermittent operation of the driven accessory. Alternatively, a plurality of differently sized input and output gears may be supported within the housing of the power take-off unit so as to provide a plurality of speed reduction gear ratios between the input gear and the output shaft. In those instances, the clutch assembly facilitates shifting between these various gear ratios.
In those power take-off units having a clutch assembly, a hydraulic control system is often provided to control the operation thereof. A typical hydraulic control system utilizes pressurized fluid from the transmission to selectively engage and disengage the clutch assembly. To accomplish this, it is known to connect a solenoid valve between a high pressure fluid port of the transmission and a clutch actuation port of the power take-off unit. When it is desired to enable operation of the driven accessory, the solenoid valve is opened to permit fluid communication between high pressure fluid port of the transmission and the clutch actuation port of the power take-off unit. In response to the application of the high pressure fluid, the clutch assembly is engaged to cause operation of the driven accessory. When it is desired to disable operation of the driven accessory, the solenoid valve is closed to prevent fluid communication between high pressure fluid port of the transmission and the clutch actuation port of the power take-off unit. In response to the removal of the high pressure fluid, the clutch assembly is disengaged to prevent operation of the driven accessory.
In the past, the solenoid valve has been provided as a separate component from both the transmission and the power take-off unit. Thus, known solenoid valves have been mounted on other portions of the vehicle, usually on a side rail of a frame assembly for the vehicle. However, such mounting on the vehicle frame assembly usually required that one or more mounting holes be drilled or otherwise formed through the side rail, which was not only time consuming but also could undesirably weaken the side rail. Furthermore, several flexible hoses were usually required to be connected between the transmission, the solenoid valve, and the power take-off unit. The use of such hoses further complicated the installation process and undesirably increased the amount of space required to be provided. Thus, it would be desirable to provide an improved structure for a power take-off unit that avoids these problems.